1. Field of the Invention
This invention relates to a cardioplegia management system for cardioplegia catheters, and more specifically, to such a cardioplegia management system for controlling flow in cardioplegia delivery tubing.
2. Description of Related Art
It has long been recognized in the field of cardiac surgery that when operating on the heart, optimum surgical conditions usually include interruption of its normal functioning. For obvious reasons, an arrested, flaccid heart is preferred during certain cardiac surgical procedures over a beating heart having ordinary blood flowing through it in the normal manner. Thus, it is often the practice to employ extracorporeal cardiopulmonary-bypass techniques in which the heart is isolated from its normal life-sustaining blood supply.
The functioning heart receives its blood supply from the left and right coronary arteries which branch directly from the aorta. About one-half to three-quarters of the heart's blood supply drains through veins flowing into the coronary sinus, which empties directly into the right atrium. A few of the heart's veins, such as the thebesian veins, open directly into the atria or ventricles of the heart.
Cardioplegia, which literally means "heart stop," protects the myocardium, the "heart muscle" as it were, during surgery and, in one technique widely employed, entails infusion of the heart with a cold cardioplegic solution by way of the veins and arteries serving the heart muscle. Typically the heart is chilled and the cold cardioplegic fluid is employed in a manner to maintain the temperature of the heart a few degrees above freezing during the operation to minimize degradation of the heart muscle.
In an alternative technique, the cardioplegic fluid comprises warm blood as a principal constituent.
In any case, cardioplegic fluids typically contain potassium, magnesium, procaine or a hypocalcemic solution, and act to arrest the beating of the heart by depolarizing cell membranes.
The cardioplegic fluid may be administered in an antegrade manner by introducing it into the coronary arteries in the normal direction of blood flow, or in a retrograde manner by introducing it into the cardiac veins in the direction opposite to the direction of normal blood flow, or in alternating retrograde and antegrade administration at the surgeon's direction.
In conventional antegrade cardioplegia, a cannula is employed which terminates in a hollow needle, the needle being inserted through the wall of the aortic root below a clamp which isolates the aorta from the extracorporeal cardiopulmonary-bypass circulatory system. The cardioplegic fluid is introduced through the hollow needle and flows through the coronary arteries in the normal direction of blood flow. Examples of appropriate cannula assemblies for this purpose are described and illustrated in U.S. Pat. No. 4,596,552, issued Jun. 24, 1986 in the name of J. H. DeVries, and U.S. Pat. No. 5,151,087, issued Sep. 29, 1992 in the name of K. R. Jonkman, both assigned to the assignee of the present invention.
Retrograde cardioplegia is conventionally administered by first inserting a balloon catheter within the coronary sinus, inflating the balloon to engage the wall of the coronary sinus and thus form a seal against backflow of fluid from the coronary sinus into the right atrium, and then perfusing the cardioplegic fluid backwards through the coronary blood vessels.
Many surgeons prefer to be able to administer either antegrade or retrograde cardioplegia as and when they choose during the course of the surgery. In such instances, a perfusion set provided with a selection system is employed to connect the antegrade and retrograde catheters to a common source of cardioplegic fluid and to alternate selectively between antegrade and retrograde delivery of the fluid to the heart.
One selection system employs a three-way switch or valve operable to direct the cardioplegia flow into either one or the other of the catheters, or, in an "off" position, to prevent flow in each of the catheters. Such a system is described and illustrated in U.S. Pat. No. 5,082,025, issued Jan. 21, 1992 in the names of J. H. DeVries et al. and assigned to the assignee of the present invention.
Some surgeons prefer instead to use a pair of Roberts-type occluding clamps, one mounted on each of the supply tubes, to select antegrade or retrograde delivery of the cardioplegia flow to the heart or to prevent flow altogether. For quick visual verification of the supply lines, the Roberts clamps may be color-coded, with one color representing antegrade delivery and another color representing retrograde delivery.